Hi,

I know this is a ford forum, but I have a chevy question, and maybe wanted to know if any of you worked on these, or what the best forum was for chevy users...

I didn't buy it, was a free car - I love my fords, but I need to get this chevy back on the road, asap...

Thanks to all!

Cheers

 

I work on GMs all the time for customers. How can I help?

 

ok!! whattcha want to know? chevy parts are cheap. i often pondered why is there 2rows of chevys and 1 row of fords? and 1/2 a row chryslers,amc,internationals, see!

 

Ok...

Engine issue...

This is the Chevy 3.1L - very common engine, used on the Montes, Olds, etc - this one is a 1993 Lumina Sedan - it's the older style 3.1L (pre OBDII

I had the top end rebuilt, and done right - I even got new remaned heads, etc (it blow a HG) so I figured why pay the labor 2x, etc... in case the alum head on that side was also warped, etc...

Ok, going down the hwy, with foot on gas, runs like a dream, like a new car... take your foot off the gas, different story...

first, it doesn't coast, but only dies down to about 45mph, and stays at like 1500RPM and then hunts a bit, and finnally falls down, but the idle is then rough...

The idle sounds like a racing engine at idle - you know, with a beefed up cam... or blower, etc... cool sounding, but not good for this car.

guy thought it was a vacuum leak - he checked and double checked everything - rechecked the intake, checked the plenum, and every hose was replaced for vacuum - no leaks...

it's tossing a MAP sensor code, but we tried like 4 maps, no dice... it's not the IAC, and he said the TPS was working correctly...

the light goes out when you give it gas

I was reading, and one thing he never checked was the fuel pressure regulator - it does have a vacuum line on it, and I'm guessing here, but wouldn't I have less pressure at the rail at idle than I would at 3000 RPM

was thinking it might also be the engine temp sensor? - but I haven't started it when the engine is cold, if it runs rough still when cold, doubt it's that, since I would think the computer is giving richer mix on a cold start, as normal... it runs rough at idle for sure, once it's warmed up...

I'm looking to rule out the Fuel Pressure Regulator - as I know I will have to pull the plenum to get at it. I can put a tester gauge on the rail (there is a valve there) - but I want to know if I should be getting less pressure at idle than I would if I held it at 2000 rpm, etc...

or, should I test for vacuum coming off of that unit, and what is being fed into the map? - the way I understand it, is that the system ignores vacuum when you are driving, but then off the gas, that's where everything vacuum wise should be working correctly...

ok, that's where I'm at... anyone? anyone? VOODOO Economics!

 

Fuel pressure and leaking injectors are the first couple things that come to mind, but if any sealant was used with those plastic and silicone gaskets, pull it apart and do it again. They need to be installed dry, no sealants, no form-a-gasket, or else there will be leaks. Just use a dab at the corners of the gaskets as instructed. Also, make sure the "new" heads have the correct angle and are actually sealing to the intake, the intake was not overtorqued as this will also cause warpage and leaks, and the seal is in place correctly between the intake halves.
The 3.1 is a PITA to seal properly, and is the subject of a few recalls for the intake gasket. Make sure the procedure is followed to the letter and it should be OK.

 

check and make sure you have manifold vaccuum at the map sensor.

 

how is it generated? - and how much should I have there? - I assume it gets generated by not have a leak anywhere else, but be as specific as you like.

can I just put a vacuum tester there? what should I have for a reading at idle?

Thanks

 

Also, this is the 3.1 that was before they ruined it :-) - the later (mid 90's) 3.1 had that intake leak problem. This was the pre-1995 version. There is a difference.

he actually replaced the lower intake, because he told me it was warped, and when he did that, it sealed then... wasn't sealing before... of course, just going by what he told me...

The only stuff he used was that black stuff for the valley, and only in the corners, in specific areas that you can see needs it... not on the gasket itself.

so, if it's a leaky injector, it's the o ring for that injector? this is leaking air or fuel? do I have to replace the whole injector, or just the O ring?

Thanks

 

also, how can I check to see if it's a fuel pressure problem?

 

yes you can put a gauge at the sensor. you should get anywhere from 17-20 inches of vaccuum.if you crack the throttle open it should drop slightly then come back up. if you have a vaccuum leak its going to be low.

 

The cheap trick here would be to start it up, let it idle, pop the hood, and spray VERY SMALL AMOUNTS of starting fluid around all of your vacuum lines and fittings, injectors, and the manifold - if the idle goes up sharply it points to a bad vac line, or fitting.

Don't go crazy with it! Let the last shot clear out, before a new shot is sprayed. I once had a brand new down vest ruined by a man who butted into a car I was checking out and sprayed stuff everywhere - causing an engine fire! Naturally, the dumb buck grabbed MY JACKET to snuff it out with... (I should have brained him with a wrench)

Failing that it reminds me of a Taurus I had once that had a computer controlled IDLE AIR BLEED device that went bad once and cost me $400.oo to have found when I couldn't make heads or tails of why the idle kept on going up.

(EFI is an SOB when it comes to labor to replace small stuff. I bet the unit only cost $29 bucks but was buried way down in there)

(Why is it the numbers "1-8-6-3-5-4-7-2" keep on coming back to haunt me? By now I should have forgot that...)

 

Hi,

this is actually what he was doing, as he was sealing all the leaks, one at a time, and trying to find it - yeah, I mean it runs like it has a vacuum leak - at least the computer thinks so...

I don't know if it's better or worse that it's only OBDI - I figured less stuff to replace, or that could go wrong...

I guess I need to see what I have for vacuum at the map first.

Still never got any answer on my fuel pressure question - this regulator uses a vacuum connection, which I'm assuming controls a diaphram when the engine builds up vacuum, (say, at idle) - and this diaphram limits the amount of fuel to the injectors, so the mixture leans out? is that how these work?

I guess the thing to do is to take it to an engine guy that has one of those big engine computers? - I don't mind paying $70 an hour to someone, if the problem can be dianosted right the first time, and fixed for that (plus parts) - I can't spend any more time guessing with this thing for sure, but I'm just trying to eliminate things too.

anything else to see if it's fuel related?

 

ps sorry for all the typos - it's late... :-)

Thanks for any and all further input.